Support variadic native function calls #1031

Summary

Add an explicit signature and call-frame mechanism for invoking C variadic functions safely.

Why

Raylib 6.0 exposes two variadic public functions, TraceLog(int, const char *, ...) and TextFormat(const char *, ...). Both remain outside the generated bindings because the current FFI can describe only a fixed argument array. See the merged skip report.

Current behavior

There is no valid descriptor for the variadic tail:

const traceLog = raylib.bind("TraceLog", {
  args: ["i32", "utf8string"],
  returns: "void",
});
traceLog(3, "%s", "hello");

The extra values are not part of the compiled signature and are not marshalled, so this cannot safely call the C function.

Current-source evidence on main (34cc32f):

• Signature parsing accepts only a fixed args array.
• Invocation allocates and marshals exactly FSignature.ArgumentCount values.
• The original FFI issue explicitly left varargs out of scope: Add explicit FFI support for native shared libraries #178.

The fresh-main FFI suite passes in interpreted and bytecode modes (92 tests, 337 assertions); it contains no variadic signature surface or fixture.

Expected behavior

Provide an explicit way to declare a fixed prefix plus variadic argument types at each call, applying the platform ABI's default argument promotions and classification rules. Calls that omit required variadic type information should fail before entering native code.

Scope notes

• Manual signature declaration is sufficient; automatic header parsing is out of scope.
• Cover C variadic calls only. Variadic native-to-JavaScript callbacks are a separate design problem.
• Related: Add explicit FFI support for native shared libraries #178, FFI v2 #827, and GocciaScript-Raylib PR #7.